U.S. Pat. No. 6,449,036 (Wollmann et al.) discloses a device wherein two lasers each generate a laser beam. The laser beams are deflected by mirrors and brought together into a common beam. For this purpose, one of the mirrors is transparent for the laser beam of the laser situated behind it. The combined laser beams pass through a hole in a further mirror and impinge on one of the plane polygon surfaces of a rotating polygonal mirror wheel. The polygonal mirror wheel guides the laser beams over a parabolic mirror, and the laser beam reflected by the parabolic mirror is guided to an inclined mirror and impinges on the surface of an object to be scanned. The object surface is projected onto the light receiver. A drawback with the device in U.S. Pat. No. 6,449,036 is that the laser is monochromatic.
WO9844335 A1 (Ruymen) discloses a device which can be mounted in a sorting apparatus. The device is provided with two light sources which each generate an intense, focused band of light. Both light sources generate light of different frequency and are brought together into a band of laser beams by a selectively semi-reflecting mirror (dichroic mirror) and an ordinary mirror. This light band is reflected towards a moving, prismatic mirror. The faces of this mirror are reflective and are set at essentially the same angle to one another. Furthermore, this prismatic mirror rotates around its central axis. The light band falling on such a face is directed towards the product to be sorted. As a result of the rotation of the mirror, the light band moves transversely across the stream of parts of the product. In doing so, said band moves each time in the same direction between two positions over the width of the stream of parts. When the light band falls on a part of the product, it is scattered and/or reflected by said part. Scattered light is at least partly captured by the same face, and, via said face, is led along approximately the same path as the light band to a beam splitter which reflects the scattered light at an angle towards two detectors. A drawback with the device in WO9844335 A1 is that the illumination is on the same optical path as the detection, whereby problems with total reflections may occur.
U.S. Pat. No. 3,176,306 relates to an apparatus for testing surface quality of material, and it discloses a “moving” slit viewing arrangement wherein a tin sheet which is again moves in a certain direction. Upper and lower light banks (line light sources) are mounted to give the desired off-specular angle of illumination and illuminate a strip of the tin sheet transverse to its direction of motion. A hood is positioned opposite the strip so as to restrict the view of a television camera to the strip.